Abstract
The oil exploration and search for new oil production fields is expanding further north and has reached the Arctic. Oil drilling activities release large amounts of produced water (PW) to the marine environment and sub-lethal effects on biota cannot be excluded. The polycyclic aromatic hydrocarbons (PAHs) present in PW have previously been shown to exhibit negative effects on growth, development and survival of aquatic organisms. The Arctic copepod Calanus glacialis is an abundant zooplankton species and holds a key position in the energy transfer from primary production to higher trophic levels. C. glacialis accumulates large volumes of lipids during late developmental stages which makes it prone to the uptake of lipophilic oil components. This study assesses the potential impact of PW-related PAHs on the metabolism of C. glacialis. In a semi-static setup, stage V C. glacialis copepodites from Kongsfjorden, Svalbard were exposed to the water soluble fraction of 11 selected PAHs (ΣPAH 7,90 μg L-1). The copepods were sampled at equal intervals during the exposure (120 h) and the following recovery (120 h). Oxygen consumption was measured in temperature-controlled glass chambers containing three C. glacialis each, using a fiber-optic oxygen meter. Dry weight, carbon and nitrogen content of the specimens were determined and body and lipid sac volumes were calculated based on biometrical measurements obtained from pictures of the C. glacialis individuals. Additionally, the PAH concentrations in the exposure media and the body burden in copepods were analyzed, in order to validate the exposure and assess the uptake and depuration of the components. No effects on C. glacialis respiration rate or body mass after PAH exposure were observed in the study. Findings revealed large variations in the measured endpoints between the specimens. The body size variations between individuals in the samples might be a consequence of depth-related difference in body size, since the copepods were collected with vertical hauls using an open net, and hence were sampled from the entire water column. Several of the PAHs showed modest or no decrease in body concentration after 5 days of recovery. The slow depuration of PAHs in C. glacialis confirmed in this experiment indicates that especially components with a high log Kow (octanol-water coefficient) may be more available for transfer to progeny, and for chronic exposure to species of higher trophic levels. These findings warrant for exposure studies with longer recovery periods to examine C. glacialis depuration rates of heavy PW components and for studies including the potential for trophic transfer. Further, this study expands the limited knowledge on possible effects on lipid-rich Arctic copepods resulting from exposure to PW components.
